Preparation of hydroxy-carboxylic acids



Patented Sept. 1, 1953 PREPARATION OF HYDROXY-CARBOXYLIG ACIDS Hans Schmidt, Wuppertal-Vohwinkel, Germany, assignor, by mesne assignments, to Schenley Laboratories, Inc., New York, N. Y., a corporation of Delaware No Drawing. Original application November 17,

1949, Serial No. 128,024. Divided and this application October 10, 1951, Serial No. 250,793. In Germany October 20, 1948 4 Claims. (Cl. 260-528) This invention relates to the production of polyhydroxymonocarboxylic acids and more particularly to a catalytic process for the oxidation of sugars. This application is a division of my copending application, Serial No. 128,024, filed November 17, 1949, entitled Hydroxy-Carboxylic Acids.

It is known that the oxidation of reducing sugars with oxygen or air in an alkaline solution can be carried out in such a manner that a polyhydroxymonocarboxylic acid having one less carbon atom, is obtained as the chief reaction product. For this purpose, oxygen or air in very finely distributed form is caused to react upon the monosaccharides in an alkaline solution.

Since the yield obtained accordin to the above process is unsatisfactory I have made efforts to influence the reaction by adding catalysts. Although the usual catalysts, e. g. metals, partly accelerate the oxidation process they have proved not to promote the formation of polyhydroxymonocarboxylic acids but to influence the oxidation in a different direction.

I have now found that certain organic compounds, particularly simple mononuclear aromatic nitroand nitroso-compounds, definitely promote the formation of polyhydroxymonocarboxylic acids, increasing the yield of these acids and reducing the formation of by-products.

The addition of small amounts of such substances 30 sufilces to catalyze the oxidation reaction in a is inverted after the addition of some hydrochloric acid. This solution, together with the oxidation catalyst as hereinafter specified, is filled into a vertical glass tube of 75 mm. diameter and oxygen, in a vigorous current is introduced through a clay filter candle at the base of the tube. From a dropping funnel mounted at the top of the tube, a solution of 147 .5 grams of caustic potash in 950 cc. of water is added dropwise over a 2 hour period. The temperature of the reaction mixture rises spontaneously and then is kept at 40-42" C. while oxygen is passed through for another 2 hours, followed by air for a further 4 hours. The progress of the oxidation can be tested, for instance, by titration. After completion of the oxidation, the solution is neutralized with glacial acetic acid and reduced to a small volume in vacuo. The potassium arabonate formed crystallizes and a further crop is obtained when methanol may be added. The reaction product is isolated, Washed with methanol, and dried.

The following table gives a summary of the yields obtained in accordance with this inven tion while using different catalytically active substances.

In order to complete the comparative tests according to the above schedule some of the experiments listed in the following table were carried out with air exclusively and some others with oxygen exclusively.

Time of lntro- Yield of ducingarabonate of potasslum in g'llIlS. (themy 180 a Quantity of the catalyst used Catalyst oxygen Hours N itrosobenzena p-Nitrobenzmc acld m-Nltrobenzoic acid.

o-Nitrophenol use-anew sumsu e:

wwwmw-oowww-me- It is evident from the data of this table that, in accordance with my invention, the yield of polyhydroxymonocarboxylic acids is considerably increased. It will be understood that, in the process of this invention it is also possible to com- 55 bine or use conjointly difierent catalysts of the group above mentioned. The efiicienoy of the catalyst is not only evident when using oxygen exclusively, or on subsequently completing the oxidation. with ain after initial, use of oxygembut also is evident when using air exclusively for the entire oxidation. This means a substantial economy in the oxygen required which is important when working on a technicalscale since a considerable part of the oxygen passes'througn unused. Without using catalysts, yields are obtained with air which are. far: belnw. those oldtained with oxygen or with; oxygen andair; (of; tests 1, 2 and 3).

The melting points (with decomposition) of the products obtained according; to the. invention are.-

between 215 and 220 C. On=conversion inter calcium arabonate, good yields: are, obtained Only a slight amount of insoluble calcium salt (cal cium oxalate) is formed, owing to the fact that the formation of by-prcducts of the oxidation process is substantially reduced. Any residual catalytic material inthe'product which may'not' have been washed outwith methanol can easily Having thus described the subject matter of thi invention, what it is desired to secure by Letters Patent is:

l. Ina process for the pnoductioniofaliphatic polyhydroxymonocarboxylic acids by oxidation of a reducing sugar with an oxygen-containing gas in an aqueous alkaline reaction medium, the improvement that comprises performing this oxid'atibn' whileliaving' present in the reaction medium, a catalytioally efiective amount of catalyst compnising; a simple mononuclear aromatic compound having a. nuclear substituent of the group consisting of nitro= and nitroso.

2. A- process asdefined in claim 1 wherein the simplezmononucleari aromatic compound is nitrobenzene.

3: Av process? as; defined in claim 1 wherein the simple-mononuclean aromatic compound is nitrosobenzene.

4. A process as defined in claim 1 wherein the simplemononuclear aromatic compound is nitrobenzoic acid;

S" SCHMIDT? References Cited in the file of this patent FOREIGN PATENTS Number Country Date" 620,248 Germany Oct. L'l,,19-35 

1. IN A PROCESS FOR THE PRODUCTION OF ALIPHATIC POLYHYDROXYMONOCARBOXYLIC ACIDS BY OXIDATIN OF A REDUCING SUGAR WITH AN OXYGEN-CONTAINING GAS IN AN AQUEOUS ALKALINE REACTION MEDIUM, THE IMPROVEMENT THAT COMPRISES PERFORMING THIS OXIDATION WHILE HAVING PRESENT IN THE REACTION MEDIUM, A CATALYTICALLY EFFECTIVE AMOUNT OF CATALYST COMPRISING A SIMPLE MONONUCLEAR AROMATIC COMPOUND HAVING A NUCLEAR SUBSTITUENT OF THE GROUP CONSISTING OF NITRO AND NITROSO. 